Point emission type light emitting element and concentrating point emission type light emitting element

ABSTRACT

To provide a point emission type light emitting element that restricts the light emitting area within a sufficiently tiny region and can be manufactured at a low cost, the point emission type light emitting element is a light emitting element that has stripe ridge comprising an n-type layer, an active layer and a p-type layer that are formed from semiconductors on a substrate, so as to emit light from one end face of the stripe ridge, wherein the stripe ridge has a protruding portion on the end face described above and the surface of the light emitting element is covered with an shading film except for the tip of the protruding portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a point emission type light emittingelement having a light emitting area restricted within a tiny region,and to a concentrating point emission type light emitting element thatconcentrates light emitted thereby and outputs the light through a tinyregion.

2. Description of the Related Art

The present applicant already developed nitride semiconductor lightemitting diodes that emit blue and green light with high output powerand are used in practical applications as light sources for large imagedisplay apparatuses. The nitride semiconductor light emitting element ismanufactured, for example, by forming p-type and n-type ohmic electrodeson a multi-layer semiconductor film that is formed from a nitridesemiconductor of GaN, AlN, InN or a mixed crystal thereof on a sapphiresubstrate, and separating the elements into chips by such processes ascleaving, RIE etching or dicing. The light emitting element made asdescribed above emits light not only from a light emitting layer butalso from cut-off surfaces and principal plane of the substrate aftercausing the light to repeat transmission through the other semiconductorlayers and in the substrate, refraction and reflection therein.

In recent years, there have been increasing demands for light emittingelements that restrict the light emitting area within a microscopicregion for such applications as the light sources for opticalcommunication, electrophotography and virtual reality display. To meetthese demands, nitride semiconductor light emitting elements of variousconstitutions have been proposed with the light emitting area restrictedwithin a microscopic region.

An end face emitting type light emitting element has been proposed as alight emitting element having microscopic light source. The end faceemission light emitting element employs double heterojunction structurewherein a light emitting layer is sandwiched by forming p-type andn-type semiconductor layers that have wide band gap, as the basicstructure similarly to a semiconductor laser. For example, an end faceemission type light emitting diode made of nitride semiconductor employsseparation-confinement heterojunction structure (SCH) based onAlGaN/GaN/InGaN.

However, in the constitution of the proposed light emitting element thatrestricts the light emitting area within a microscopic region, a highaccuracy of patterning is required to restrict the light emitting areawithin the microscopic region, and an advanced photolithographytechnology must be used. This results in the problem that the lightemitting element that restricts the light emitting area within themicroscopic region cannot be provided at an economical price.

Although the end face emission type light emitting diode can be madewith small spot size, multi-mode light emission is produced since lightis emitted not only from the end face of the light emitting layer butalso from the end faces of the n-type semiconductor layer formed nearerto the substrate than the light emitting layer, thus making itunsuitable for such applications as a single spot of good near-fieldpattern is required.

SUMMARY OF THE INVENTION

Thus, a first object of the present invention is to provide a pointemission type light emitting element that restricts the light emittingarea within a sufficiently tiny region and can be manufactured at a lowcost, and a method of manufacturing the same.

A second object of the present invention is to provide a concentratingpoint emission type light emitting clement that produces a single spotlight of good near-field pattern with a high efficiency of lightemission.

The point emission type light emitting element according to the presentinvention to meet the first object described above is a light emittingelement that has stripe ridge comprising an n-type layer, an activelayer and a p-type layer that are formed from semiconductors on asubstrate, so as to emit light from one end face of the stripe ridge,wherein the stripe ridge has a protruding portion on the end facedescribed above and the surface of the light emitting element is coveredwith an shading film except for the tip of the protruding portion.

In the point emission type light emitting element of the presentinvention constituted as described above, since the surface of the lightemitting element is covered with the shading film except for the tip ofthe protruding portion, light emitting area can be restricted to the tipof the protruding portion.

Therefore, according to the present invention, light can be emitted onlyfrom the tip of the protruding portion, and the light emitting area canbe made extremely small by setting the width of the protruding portionin accordance to the light emitting area that is required.

Also because the surface of the light emitting element is covered withthe shading film except for the tip of the protruding portion, leakageof light from other portions than the tip of the protruding portion canbe suppressed, thereby increasing the efficiency of light emission.

Also the n-type layer, the active layer and the p-type layer of thepoint emission type light emitting element of the present invention canbe formed from nitride semiconductors, which makes it possible to emitlight of relatively short wavelength.

The method of manufacturing the point emission type light emittingelement according to the present invention is, in order to achieve thefirst object described above, a method of manufacturing the pointemission type light emitting element by forming a plurality of elementson the substrate and dividing the substrate with layers formed thereoninto individual elements, and comprises a step of forming the n-typelayer, the active layer and the p-type layer on the substrate one onanother, a step of forming stripe ridge that has a neck portion formednear one end thereof having narrower width than the other portion incorrespondence to the elements described above, a step of formingshading films at least on one end face of the stripe ridge and the topsurface and both side faces of the neck portion, and a step of dividingthe elements at the neck portion along a direction perpendicular to thelongitudinal direction of the stripe ridge.

According to the method of manufacturing the point emission type lightemitting element of the present invention constituted as describedabove, the light emitting element having the light emitting arearestricted within a tiny region located at the end of the stripe ridgecan be easily manufactured, and the light emitting area that hasextremely small light emitting area can be manufactured at a low cost.

The concentrating point emission light emitting element according to thepresent invention to meet the second object described above is a surfaceemission type light emitting element made in stacked semiconductorstructure of double heterojunction structure wherein an active layer issandwiched by a p-type semiconductor layer and an n-type semiconductorlayer that have band gap larger than that of the active layer so as toemit light from a light emitting point located in the surface of thep-type semiconductor layer, where such a pyramidal surface is providedin the stacked semiconductor structure located right below the lightemitting point that reflects the light upward or retracts the light, thestacked semiconductor structure is divided into a plurality of lightemitting regions located around the pyramidal surface that is at thecenter, and ridges of smaller width than the light emitting region are sformed on the p-type semiconductor layer so that light emitted from thelight emitting regions is directed toward the pyramidal surface.

In the concentrating point emission type light emitting element of thepresent invention constituted as described above, since the waveguide isformed in each of the light emitting regions, that light emitted in thelight emitting regions is directed toward the light emitting point so asto be reflected or refracted by the pyramidal surface and is outputthrough a narrow region, and therefore the element can be used as apoint light source.

The concentrating point emission type light emitting element of thepresent invention is also capable of emitting light with a highluminance since light emitted in all light emitting regions isconcentrated and output together.

Moreover, since the concentrating point emission type light emittingelement of the present invention can concentrate light into a smallregion and output the light therefrom, a light spot of single modehaving good near field pattern can be produced.

In the concentrating point emission type light emitting element of thepresent invention, the plurality of light emitting regions can be formedby separating the light emitting regions from each other by etching theborders between adjacent light emitting regions to a depth midway in then-type semiconductor layer in the stacked semiconductor structure exceptfor the light emitting point and a vicinity thereof, and forming n-typeelectrode on the n-type semiconductor layer that has been exposed byetching.

In the concentrating point emission type light emitting element of thepresent invention, the pyramidal surface can be constituted from apyramidal cavity that has an apex located in the light emergingdirection and is formed in the stacked semiconductor structure.

Moreover, in the concentrating point emission type light emittingelement of the present invention, the pyramidal surface can also beformed by filling a recess of pyramidal shape, that expands toward thelight emerging point and is formed so as to reach at least the n-typesemiconductor layer in the stacked semiconductor structure, with atransparent material having a refractive index higher than that of theactive layer.

In the concentrating point emission type light emitting element of thepresent invention, the pyramidal surface is preferably a conicalsurface, which makes it possible to produce spot light of near truecircle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the constitution of a nitridesemiconductor light emitting element according to first embodiment ofthe present invention.

FIG. 2 is a perspective view after nitride semi conductor layer thatconstitutes the element is formed on a sapphire substrate in themanufacturing process of the nitride semiconductor light emittingelement according to the first embodiment of the present invention.

FIG. 3 is a perspective view after a ridge stripe and element regionsare formed by etching in the manufacturing process of the nitridesemiconductor light emitting element according to the first embodimentof the present invention.

FIG. 4 is a perspective view after a p-type electrode and an n-typeelectrode are formed in the manufacturing process of the nitridesemiconductor light emitting element according to the first embodimentof the present invention.

FIG. 5 is a perspective view after a p pad electrode and an n padelectrode are formed in the manufacturing process of the nitridesemiconductor light emitting element according to the first embodimentof the present invention.

FIG. 6 is a perspective view after an shading film is formed to coverthe top surface of the element in the manufacturing process of thenitride semiconductor light emitting element according to the firstembodiment of the present invention.

FIG. 7 is an enlarged perspective view showing the end of the ridgestripe in the nitride semiconductor light emitting element according tothe first embodiment of the present invention.

FIG. 8 is a partial plan view of a concentrating point emission typelight emitting element according to second embodiment of the presentinvention.

FIG. 9 is a sectional view taken along lines A-A′ of FIG. 8.

FIG. 10 is a sectional view taken along lines B-B′ of FIG. 8.

FIG. 11 is a sectional view of stacked semiconductor structure grown inthe manufacturing process of the concentrating point emission type lightemitting element according to the second embodiment of the presentinvention.

FIG. 12 is a plan view of the stacked semiconductor structure afterforming a light emitting region therein in the manufacturing process ofthe concentrating point emission type light emitting element accordingto the second embodiment of the present invention.

FIG. 13 is a plan view after forming a ridge in each light emittingregion in the manufacturing process of the concentrating point emissiontype light emitting element according to the second embodiment of thepresent invention.

FIG. 14 is a plan view after forming a p-type electrode in each lightemitting region and an n-type electrode between adjacent light emittingregions in the manufacturing process for the concentrating pointemission type light emitting element according to the second embodimentof the present invention.

FIG. 15 is a plan view after forming an insulation film 113 that fillsthe light emitting region in the manufacturing process for theconcentrating point emission type light emitting element according tothe second embodiment of the present invention.

FIG. 16 is a plan view after forming p pad electrodes that connect thep-type electrodes of all light emitting regions in the manufacturingprocess for the concentrating point emission type light emitting elementaccording to the second embodiment of the present invention.

FIG. 17 is a plan view showing the electrodes arrangement in theconcentrating point emission type light emitting element according tothe second embodiment of the present invention.

FIG. 18 is a sectional view showing the constitution of a refractingpyramidal surface of a variation according to the present invention.

FIG. 19 is a plan view showing the light emitting region of a variationaccording to the present invention.

FIG. 20 is a sectional view showing the constitution of a cavity 152 b(opening at the top) of a variation according to the present invention.

FIG. 21 is schematic sectional view showing the state of emitting lightin the case of using a cavity closed at the top (a) and in the case ofusing a cavity open at the top (b)

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now the point emission type light emitting element according topreferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

Embodiment 1

The point emission type light emitting element according to the firstembodiment of the present invention is a nitride semiconductor lightemitting diode. The point emission type light emitting element has sucha constitutions as an n-type layer 12, an active layer 13 and a p-typelayer 14 that are formed from nitride semiconductors on a substrate 10made of sapphire via a buffer layer 11, with a stripe ridge 20 that hasa protruding portion 21 a being formed on one end face thereof, whilebeing covered with an shading film 31 substantially entirely except forthe tip of the protruding portion 21 a, as shown in FIG. 1. The pointemission type light emitting element is manufactured as described below.

First, as shown in FIG. 2, the buffer layer 11 made of GaN grown at alow temperature, for example, the n-type layer 12 made of GaN doped withSi, for example, the active layer 13 made of InGaN, for example, and thep-type layer 14 made of GaN doped with Mg, for example, are formedsuccessively on the substrate 10.

Then stripe ridges 20 are formed in regions that correspond to theelements, and 2-step etching operation is carried out as described belowin order to define the element regions.

In the first etching process, a first mask is formed in a region wherethe stripe ridge 2—would be formed, and the portion not covered by thefirst mask is etched by reactive ion etching (RIE) midway in depth ofthe n-type layer 12. The first mask used in the first etching process isformed in such a configuration as portions that correspond to front andback sides of a cleavage surface located on one end of the stripe ridge20 are made narrower than the other portions, so that a narrow neckportion 21 is continuously formed on the end face of the stripe ridge 20after etching.

Longer axis of the stripe ridge 20 and longer axis of the neck portion21 preferably agree with each other.

Width of the stripe ridge is not limited to a particular value, but ispreferably in a range from 1 to 100 μm, and more preferably in a rangefrom 5 to 50 μm. When the width is less than 1 μm, it is difficult toprecisely form the stripe ridge 20 and the narrower neck portion 21 byetching. When the width is greater than 100 μm, loss of light due to thenitride semiconductor increases when the light generated in the activelayer is directed through the ridge 20 that is wider. When the width is5 μm or greater, the stripe ridge 20 and the narrower neck portion 21can be formed precisely by etching, and width within 50 μm makes itpossible to minimize the loss of light and cause the light to emergethrough one end face. The width is set to 20 μm in this embodiment.

According to the present invention, there is no limitation to the widthof the neck portion 21 that can be determined by setting the stripewidth and particularly the width of the end face that is obtained at thelast, so that a light source of desired small size can be formed. Stripewidth at the neck portion 21 is preferably set in a range from 1 to 10μm. When the width is less than 1 μm, it is difficult to precisely formthe neck portion 21 by etching. Width greater than 10 μm is not suitablefor the tiny light source. Width of the neck portion 21 is set in arange from 2 to 3 μm in this embodiment. According to the presentinvention, there is also no limitation to the length of the neck portion21 that can be set so that it is convenient for cleaving operation toobtain the end face. Specifically, the length is preferably set in arange from 1 to 50 μm, and more preferably in a range from 5 to 30 μm.When the length is less than 1 μm, there arises a problem related to theaccuracy in etching. Length of 5 μm or larger makes it possible tocleave at the neck portion 21 where there is less probability of defectsbeing included. When cleaving a material such as sapphire that isdifferent from the nitride semiconductor, there is a possibility ofcleaving to take place at a wrong place, and a length less than 5 μmincreases the possibility of much cleavage defects to occur in the neckportion 21, that can be reduced by setting the length to 5 μm or larger.Although cleavage can be carried out without increasing the number ofcleavage defects when the length is larger than 50 μm, this reduces thenumber of chips produced per wafer. When the length is 30 μm or less,good cleavage and satisfactory yield of production can be achieved,while securing a certain number of chips produced per wafer. The lengthis set to 10 μm in this embodiment.

In the second etching process, a second mask is formed over the areaexcept for the separation regions where the elements are to be divided,leaving the first mask used in the first etching process to remain, andthe nitride semiconductor layer is removed from the separation regionsby etching midway in depth of the buffer layer 11 or to the surface ofthe substrate 10.

Thus the 2-step etching process results in the element regions eachhaving the stripe ridge 20 and the neck portion 21 being formed incorrespondence to the elements to be separated (FIG. 3).

Then as shown in FIG. 4, a p-type ohmic electrode 41 is formed on thep-type layer 14 of the stripe ridge 20, and an n-type ohmic electrode 43is formed on the surface of the n-type layer that is exposed on theoutside of one side face of the stripe ridge 20.

The entire surface of the wafer is covered with a SiO₂ film (not shown)except for the top surface of the p-typo ohmic electrode 41 and the topsurface of the n-type ohmic electrode 43 of each electrode region. Thena p pad electrode 42 is formed in contact with the p-type ohmicelectrode 41 that is exposed through the opening in the SiO₂ film, andan n pad electrode 44 is formed in contact with the n-type ohmicelectrode 43 that is exposed through the opening in the SiO₂ film (FIG.5).

As shown in FIG. 5, the n pad electrode 44 is formed so as to overlapwith the n-type ohmic electrode 43, and the p pad electrode 42 is formedso as to make contact with p-type ohmic electrode on the top surface ofthe stripe ridge 20 and extend therefrom over the other side face of thestripe ridge 20 and over the SiO₂ film located on the outside of theside face.

Then a mask is formed to cover the n pad electrode 44 and the vicinitythereof and the p pad electrode 42 and the vicinity thereof. The mask isused to form a metal film (shading film) of Cr/Au (Au film formed over athin film of Cr) covering the entire wafer with a vapor deposition orsputtering apparatus. Thus the shading film 31 is formed to coversubstantially the entire surface of the wafer including one side face ofthe stripe ridge 20 and both side faces of the neck portion 21.

At this time, the top surface of the wafer is covered by either the npad electrode 44, the p pad electrode 42 or the shading film 31 exceptfor the small areas of the n pad electrode 44 and the vicinity thereofand the p pad electrode 42 and the vicinity thereof.

The shading film 31, the n pad electrode 44 and the p pad electrode 42are electrically isolated around the n pad electrode 44 and around the ppad electrode 42.

Then the wafer is divided into individual elements and the shading film31 is formed on the side faces of the substrate 10 after separation.

The wafer having the shading film 31 formed on the top surface thereofis stuck on a heat sensitive sheet with the electrode surface (topsurface) facing the sheet, and the wafer is scribed on the back surface.

The scribe line perpendicular to the longer side of the ridge stripe 20is formed at such a position as cross the neck portion 21 at rightangles at the center of the neck portion 21.

After sticking the scribed back surface of the wafer onto a die bondingsheet, the heat sensitive sheet is peeled off the wafer surface.

The individual element chips are separated from each other with a spaceproduced in between by pulling the die bonding sheet to expand evenly inall directions.

The end face at the tip of the protruding portion 21 a of each chip thathas been separated is a cleavage surface created after forming theshading film 31 on the top surface of she wafer, and therefore is notcovered by the shading film.

Then the electrode surfaces of the chips are pressed against an adhesivelayer of an adhesive sheet, with the adhesive layer being 10 μm thick,to be stuck thereon while maintaining the distance between the chips,and the die bonding sheet is removed. At this time the chips arearranged on the adhesive sheet in an array with a predetermined distancefrom each other and the hack surface of the sapphire substrate 11 facingup. Each chip is secured onto the adhesive sheet with the electrodesurface being pressed against the adhesive layer with a relatively largeforce, while providing masking function to prevent the shading film frombeing formed on the top surface of the chip, particularly on the endface of the protruding portion 21 a of each chips during the process offorming the shading film on the back surface and the side faces of thesubstrate.

Then the chips arranged on the adhesive sheet in an array with apredetermined distance from each other with the back surface of thesubstrate facing up are set in a vapor deposition or sputteringapparatus, where a Cr film (600 Å thick, for example) and an Au film(2400 Å thick, for example) are formed successively, thus forming theshading film 31 on the back surface and the side faces of the substrate.

In the process described above, the nitride semiconductor light emittingelements are manufactured in the form of separated chips that aresubstantially totally covered, except for the end face of the protrudingportion 21 a formed to protrude from one end face of the stripe ridge20, by either the n pad electrode 44, the p pad electrode 42 or theshading film 31 that shield light.

This provides the point emission type light emitting element that iscapable of emitting light on one end face of the stripe ridge, orfurther from limited region of the end face of the protruding portion 21a.

The point emission type light emitting element of the first embodimentthat emits light from the end face of the protruding portion 21 a allowsit to easily restrict the light emitting area within an extremely smallregion by forming the protruding portion 21 a with a small width.

That is, while it is difficult to restrict the light emitting area byforming the shading film in a predetermined pattern on the end face ofthe stripe ridge, the constitution and the manufacturing method of thefirst embodiment makes it possible by a unique technique as follows: thenarrow neck portion 21 is continuously formed on the end face of thestripe ridge and cleavage is carried out at the neck portion 21 afterforming the shading film, and the light emitting area is restrictedfurther within a narrow region on the light emitting end face of thestripe ridge, so that the light emitting area can be easily restrictedwithin an extremely small region.

While the first embodiment has been described above, the presentinvention is not limited to the first embodiment and variousmodifications can be made and various materials can be used as describedbelow.

Variation of Embodiment 1

For the substrate used in the present invention, insulating substratesuch as sapphire or spinel (MgAl₂O₄) that has principal plane in Cplane, R plane or A plane, SiC (including 6H, 4H, 3C), ZnS, ZnO, GaAs,Si and oxide substrate that makes lattice matching with nitridesemiconductor have been known as materials different from nitridesemiconductor. Sapphire and spinel are preferably used. A nitridesemiconductor substrate such as GaN and AlN can also be used.

As the nitride semiconductor formed on the substrate, III-V groupgallium nitride compound semiconductor materials can be used. Forexample, In_(x)Al_(y)Ga_(1−x−y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1), and InAlGaBN,InAlGaNP and InAlGaNAs made by adding B to the III group element orsubstituting a part of V group element N with As or P can be used. Goodlight emitting layer can be obtained by using In_(u)Al_(v)Ga_(1−u−v)N(0<u<1,0≦v<1, 0≦u+v<1). As the n-type impurity used for the nitridesemiconductor of the present invention, IV group element such as Si, Ge,Sn, S, O, Ti or Zr, or VI group element nay be used. Good carrier can begenerated by preferably using Si, Ge and Sn, and most preferably usingSi. While there is no limitation to the p-type impurity, Be, Zn, Mn, Cr,Mg or Ca may be used, and Mg is preferably used. Thus the n-type nitridesemiconductor and the p-type nitride semiconductor that constitute then-type layer and the p-type layer can be formed.

The relationship between the stripe ridge 20 and the neck portion 21 inthe present invention is not limited to the configuration shown in FIG.3, making the neck portion 21 narrower than the ridge stripe 20 so as toform the tiny light source of the desired shape and size on the neckportion.

That is, while the stripe ridge 20 and the neck portion 21 may be formedas a stripe of substantially uniform width as shown in FIG. 3, thestripe may also be formed in a tapered configuration with the widththereof varying with the position along the longitudinal direction.Specifically, the stripe may be formed in such a tapered configurationas the width of the stripe ridge 20 decreases toward the neck portion 21and the end face along the longitudinal direction, thereby increasingthe efficiency of extracting light by concentrating the light emitted bythe stripe ridge 20 into the neck portion 21. The stripe ridge 20 may betapered over the entire length thereof or in a section thereof, forexample from the joint with the neck portion 21 over some length alongthe stripe 20, as in the example described above. Similar configurationmay be employed also for the neck portion 21.

Although the ridge stripe of the present invention is formed midway indepth of the n-type layer 12 as shown in FIG. 3, the present inventionis not limited to this configuration, and the ridge stripe 20 may beformed by etching to such a depth that does not reach the active layer13. When the ridge stripe 20 is formed above the active layer 13, such astructure can be formed as degradation of the active layer 13 due toexposure to atmosphere is retarded. The effect of preventing degradationof the active layer 13 becomes more conspicuous when the stripe isformed with a small width of 10 μm or less. On the other hand, since adesired tiny light source is made by using one end face of the neckportion 21 as a light emerging surface, it is preferable to etch intosuch a depth that reaches the n-type layer, deeper than the active layer13. Etching depth in the neck portion 21 and in both sides of the striperidge 20 may be changed according to the functions thereof.

While the stripe ridge 20 and the neck portion 21 join at a surfacesubstantially perpendicular to the longitudinal direction of the striperidge 20, the present invention is not limited to this configuration.The stripe ridge 20 and the neck portion 21 may also be joined at asurface having an angle less than 90° from the longitudinal direction sothat, for example, the joint is also tapered. This configuration makesit possible to efficiently direct light from the stripe ridge 20 to theneck portion 21, and improve the efficiency of extracting light bydecreasing the loss of light due to reflection at the joint.

There is no limitation to the shading film that may be made of anymaterial as long as the light emitted by the light emitting element canbe shielded, and TiO and SiO that absorb light and metals such as Cr,Ti/Pt, Ti, Ni, Al, Ag and Au may be used. Also at least one kindselected from among a group consisting of SiO₂, TiO₂, ZrO₂, ZnO, Al₂O₃,MgO and polyimide may be used to form a multi-layer dielectric filmcomprising films λ/4 n thick (λ is wavelength and n is the refractiveindex of the material) of such a material.

Furthermore, the present invention is not limited to nitridesemiconductor.

According to the present invention, as described above, variousmodifications and various materials can be used to achieve the effectsof the first embodiment.

Embodiment 2

Now a concentrating point emission type light emitting element accordingto the second embodiment of the present invention will be describedbelow with reference to the accompanying drawings.

The concentrating point emission type light emitting element of thesecond embodiment has a plurality of light emitting regions 200 formedin radial direction around a light emitting point 150 located at thecenter thereof as shown in FIG. 8, so that light emitted by the lightemitting regions 200 is directed through waveguides formed in the lightemitting regions 200 to near the center of the radial configuration andemerges from the light emitting point 150.

In the concentrating point emission type light emitting element of thesecond embodiment, the light emitting regions 200 are formed by etchinga stacked semiconductor structure, consisting of a buffer layer 102, ann-type contact layer 103, an n-type cladding layer 104, an active layer105, a p-type cladding layer 106 and a p-type contact layer 107 formedone on another successively on a substrate 101, until the n-type contactlayer 103 is exposed in a radial pattern with the light emitting point150 located at the center thereof (FIG. 8 through FIG. 10).

Thus a plurality of the light emitting regions 200 having the stackedsemiconductor structure are formed, consisting of the buffer layer 102,the n-type contact layer 103, the n-type cladding layer 104, the activelayer 105, the p-type cladding layer 106 and the p-type contact layer107 formed one on another successively on the substrate 101, where thewaveguides are directed toward the light emitting point 150 radially,with the n-type contact layer 103 being exposed between adjacent lightemitting regions 200 (FIG. 8, FIG. 10).

According to the second embodiment, the active layer 105 is made ofInGaN, for example, while the n-type cladding layer 104 and the p-typecladding layer 106 are made of AlGaN, for example, that has larger bandgap than the active layer 105, and the light emitting regions 200 havedouble heterojunction structure. In the second embodiment, the activelayer 105 can be formed in various structures such as multiple quantumwell structure and single quantum well structure, and the mixing ratioof Al in the n-type cladding layer 104 and in the p-type cladding layer106 may be set to an appropriate value by taking account of such factorsas the confinement of light in the longitudinal direction Furtheraccording to the second embodiment, in order to improve thecrystallinity, a base layer may be formed by lateral growth so as toform the n-type cladding layer 104, the active layer 105 and the p-typecladding layer 106 thereon.

In the light emitting regions 200 of the concentrating point emissiontype light emitting element of the second embodiment, a ridge 130 isformed by etching the p-type semiconductor layers (the p-type claddinglayer 106 and the p-type contact layer 107) on both sides thereof midwayin depth of the p-type cladding layer 106 so that the middle portion ofa predetermined width remains, and a p-type electrode 111 is formed tomake ohmic contact only with the top surface of the ridge 130 (surfaceof the p-type contact layer 107 in the ridge 130) via an opening of theinsulation film 108 (FIG. 8, FIG. 10).

With this constitution, the active layer located right below the ridge130 has an effective refractive index higher than that of the activelayer on both sides thereof so that light is confined right below theridge 130 and is directed along the ridge 130.

Width of the ridge is preferably set in a range from 1 to 5 μm, morepreferably in a range from 1.5 to 3 μm, in order to effectively directthe light.

Confinement of light in the direction of depth is achieved bysandwiching the active layer 105 with the n-type cladding layer 104 andthe p-type cladding layer 106 that have lower refractive index.

According to the second embodiment, it is preferable to form a mirrorfilm for reflecting the light on the end face (used for monitoring andtherefore hereinafter referred to as monitoring end face) locatedopposite to the light emitting point 150 of the light emitting region200. The mirror film formed on the monitoring end face makes it possibleto reduce the loss caused by unnecessary radiation and improve theefficiency of light emission, since light reflected on the end face canbe output through the light emitting point 150. In the case of thisconstitution, light reflected on the monitoring end face can beamplified and output through the light emitting point depending on theconditions, so that more effective light emission can be achieved. Themirror film may be a multi-layer electric film made of SiO₂ and TiO₂,with the film thickness preferably set to nλ/4 (n=1, 2, 3 . . . , λ iswavelength of light in the dielectric material), and preferably consistof two or more pair of the layers in order to achieve satisfactoryreflection characteristic. Further in the second embodiment, it ispreferable to form the mirror film from the same material as theinsulation film 113 at the same time therewith in the same process, soas to simplify the manufacturing process and reduce the manufacturingcost.

According to the second embodiment, the n-type electrode 112 is formedon the n-type contact layer 103 that is exposed between adjacent lightemitting regions 200 (FIG. 8, FIG. 10).

Also according to the second embodiment, a cavity 152 of conical shapethat has an apex located in the direction of emerging light is formed inthe stacked semiconductor structure right below the light emitting point150 as shown in FIG. 9, so that light emitted in the light emittingregions 200 is reflected on the conical surface 153 of the cavity 152upward and is output through an opening (the light emitting point 150)of the p-type electrode 111.

Now the method of manufacturing the concentrating point emission typelight emitting element of the second embodiment will be described belowby making reference to examples of materials to be used.

(Process to Form a Mask 151)

According to this manufacturing method, a mask 151 is formed for thepurpose of forming the cavity 152 on the substrate 101 as shown in FIG.11.

According to the second embodiment, while insulating substrate such assapphire or spinel (MgAl₂O₄) that has principal plane in C plane, Rplane or A plane, or semiconductor substrate such as SiC (including 6H,4H, 3C), Si, Zn, GaAs, GaN may be used, sapphire substrate or GaNsubstrate that can be grown with good crystallinity is preferably usedwhen nitride semiconductor is employed.

The substrate 101 is preferably made of a material that has a refractiveindex higher than that of the semiconductor layer to be formed thereonby 0.2 or more.

The mask 151 is exposed to a high temperature of 1000° C. or higher whengrowing semiconductor layers in the following process, and thereforemust be made of a material that does not decompose at such temperaturesand does not allows the semiconductor to grow thereon. As such, SiO₂,SiN, W or the like can be used.

The mask 151 is preferably formed in a round (cylindrical) shape, whichmakes it possible to form the cavity 152 of conical shape in the stackedsemiconductor structure that produces spot light of near true circle.

While diameter of the mask 151 is determined according to the requiredspot diameter, the mask diameter is preferably set in a range from 0.5to 20 μm, more preferably in a range from 1 to 10 μm in order to obtainsatisfactory light of single mode.

(Process to Grow the Semiconductor Layers)

Then the buffer layer 102 having thickness of 200 Å made of GaN, forexample, an n-type contact layer 103 a made of GaN having thickness of 4μm doped with 4.5×10¹⁸/cm³ of Si, for example, an n-type cladding layer104 a made of Al_(0.1)Ga_(0.9)N having thickness of 1 μm doped with1×10¹⁸/cm³ of Si, for example, an active layer 105 a made ofTn_(0.37)Ga_(0.63)N having thickness of 0.09 μm, for example, a p-typecladding layer 106 a made of Al_(0.1)Ga_(0.9)N having thickness of 0.5μm doped with 2×10¹⁸/cm³ of Mg, for example, and a p-type contact layer107 a made of p-type GaN having thickness of 150 Å doped with 1×10¹⁸/cm³of Mg, for example, are formed successively on the substrate 101 havinga mask formed thereon (FIG. 11).

Through the process described above, the stacked semiconductor structurehaving the cavity 152 of conical shape is formed on the mask 151 asshown in FIG. 11.

(Etching for Forming the Light Emitting Regions)

Then an SiO₂ film having thickness of 0.5 μm is formed on the stackedsemiconductor structure by the plasma CVD process. This is followed bythe formation of a plurality of fan shaped patterns in radialarrangement with the apex located at the center of the mask 51 byphotolithography technique, with the SiO₂ film being etched by, forexample, RIE process The plurality (48 in this embodiment) of fan shapedlight emitting regions 200 are formed by etching the portions notcovered by the SiO₂ film by, for example, the RIE process until then-type contact layer 103 is exposed (FIG. 5). All the light emittingregions 200 are formed to have the same radial dimension and apex angleof the fan shape, and are connected to each other at the apex. The maskmay be made of a material other than SiO₂ film, such as dielectricmaterial including SiN or photo-resist material. Further, the mask maybe formed by a process other than the plasma CVD, such as magnetronsputter or ECR process.

(Formation of the Ridge)

After forming an etching mask (made of SiO₂, for example) of uniformwidth (for example, 2 μm wide and 0.5 μm thick) for forming the ridgeson the top surfaces of the light emitting regions 200, both sides of theetching mask are etched away midway in depth of the p-type claddinglayer 106, thereby to form the ridges 130 in the light emitting regions200 (FIG. 13).

(Formation of the P-Type Electrode)

Then an insulation layer 8 (for example, ZrO₂ film having thickness of0.2 μm or less) is formed to cover the portions other than the topsurfaces of the ridges in the light emitting regions 200, and the p-typeelectrodes 111 are formed so as to make ohmic contact with only the topsurfaces of the ridges that are exposed as shown in FIG. 14.

The p-type electrodes III are formed from Ni (100 Å)/Au (1500 Å), forexample, that can make good ohmic contact with the p-type GaN layer.

(Formation of the N-Type Electrode)

Then the n-type electrode 112 is formed on the n-type contact layer 103that has been exposed between the adjacent light emitting regions (FIG.14).

The n-type electrode 112 is formed from Ti (100 Å)/Al (5000 Å), forexample, that can make good ohmic contact with the n-type GaN layer.

The n-type electrode 112 is formed over the entire surface of the n-typecontact layer 103 (over-all electrode section) on the outside, with apredetermined distance in between, of the outer periphery (external arc)of the light emitting regions (outside of a circle having a radius alittle larger than the radial dimension of the fan shaped light emittingregions). Plural n-type electrodes 112 formed between the light emittingregions are electrically connected with each other on the over-allelectrode section. After forming the n-type electrodes, it is preferableto apply annealing at a temperature not higher than 700° C.

The over-all electrode section is used for the connection with outsidecircuits.

(Formation of the Insulation Film 113)

Then the insulation film 113 is formed to fill the space between thelight emitting regions, so as to entirely cover the n-type contact layer103 that is exposed between the light emitting regions except for thetop surface of the p-type electrode 111 (FIG. 10, FIG. 15).

The insulation film 113 is formed so as to cover part of the innerperiphery and outer periphery of the over-all electrode section of then-type electrode 112. That is, the insulation film 113 is formed so asto expose the main part the over-all electrode section of the n-typeelectrode 112, and the exposed portions of the over-all electrodesection is used for the connection with outside circuits.

In the second embodiment, the insulation film 113 also serves as themirror film located at the end face of the light emitting regions 200,and is therefore formed as a multi-layer film combining a low refractiveindex material layer and a high refractive index material layer, forexample, a multi-layer film of dielectric materials comprising two ormore pairs of (SiO₂/TiO₂). This constitution allows it to increase thereflectivity by increasing the number of pairs of layers. While SiO₂ isused as the low refractive index material and TiO₂ is used as the highrefractive index material to form the multi-layer film that constitutesthe insulation film 113 in the example described above, the presentinvention is not limited to this constitution and the followingmaterials may also be used to form the multi-layer film that serves asthe mirror film. For the low refractive index material layer, MgO₂,Al₂O₃, SiON, MgO and the like can be used besides SiO₂. For the highrefractive index material layer, ZrO₂, Nb₂O₅, Ta₂O₅, SiN_(x), AlN, GaNand the like can be used besides TiO₂. By combining these materials, themulti-layer film of dielectric materials that does not absorb the lightof the emission wavelength can be formed.

(Formation of the p Pad Electrode)

Then a p pad electrode 121 is formed as shown in FIG. 16 that comprisesa portion 121 a of round shape (a circle having a radius substantiallyequal to the radial dimension of the fan shaped light emitting regionwith the center at the light emitting point) for connecting the exposedp-type electrode 111 and a pad portion 121 b that is connected to theround portion 121 a via the neck portion 21 c. The p pad electrode isformed from Ni (1000 Å)/Ti (1000 Å)/Al (8000 Å), for example.

(Formation of the N pad Electrode)

Then the n pad electrode 122 is formed on the n-type electrode 112 thathas been exposed, for the purpose of bonding for electrical connectionto the n-type electrode 112. The n pad electrode is formed from Ni (1000Å)/Ti (1000 Å)/Al (8000 Å), for example.

The concentrating point emission type light emitting element of thesecond embodiment that has the electrode arrangement shown in FIG. 17 ismanufactured as described above.

Since the concentrating point emission type light emitting element ofthe second embodiment that has the constitution described above has thewaveguide formed in each light emitting region, light emitted from thelight emitting regions 200 is directed through the waveguide toward thelight emitting point, reflected on the conical surface of the cavity 152and is output through the light emitting point 150 that is the openingformed in the p-type electrode.

With this constitution, since light emitted from the light emittingregions 200 is concentrated at the light emitting point 150 and isoutput therefrom, light emission with high luminance is achieved.

Also in the concentrating point emission type light emitting element ofthe second embodiment, since the reflector surface having conical shapeis constituted from the cavity 152 of conical shape, spot light of neartrue circle can be obtained.

Also in the concentrating point emission light emitting element of thesecond embodiment, the cavity 152 of extremely small conical shape ofthe diameter of the circular mask 151 can be easily formed, andsatisfactory spot light of single mode can be obtained.

Since the concentrating point emission type light emitting element ofthe second embodiment has the stacked semiconductor structure formedwith the gallium nitride compound semiconductor element, spot light ofrelatively short wavelengths such as yellow, blue and violet colors aswell as ultraviolet region can be obtained.

Variation of Embodiment 2

Although the reflector surface having conical shape is constituted fromthe cavity 152 of conical shape in the second embodiment, the presentinvention is not limited to this constitution and a refracting surfacehaving conical shape may be formed as described below, so thatconcentrated light is output from the light emitting point.

Specifically, as shown in FIG. 18, in the stacked semiconductorstructure located right below the light emitting point, such a recess ofpyramidal shape is formed so as to reach at least the n-typesemiconductor layer that expands toward the light emerging point, andthe recess is filled with a transparent material 152 a that has arefractive index higher than that of the active layer.

With the constitution described above, light emitted in the lightemitting regions and directed toward the light emerging point isrefracted due to the difference in the refraction index between thesemiconductor layer (mainly the active layer) and the transparentmaterial 152 a that has a high refractive index in the conical surfaceof the recess, so as proceed upward in the transparent material 152 a.

Thus light is output through the light emitting point 150 upward.

Effects similar to those of the second embodiment can also be achievedwith the constitution described above.

Although the light emitting regions are formed in straight linesarranged radially around the light emitting point at the center in thesecond embodiment, the present invention is not limited to thisconfiguration and curved light emitting regions 201 may be formed asshown in FIG. 19.

Effects similar to those of the second embodiment can also be achievedand the light emitting regions may be made longer with the constitutiondescribed above.

Although the concentrating point emission light emitting element of thesecond embodiment is made in such a constitution that has the lightemitting regions of double heterojunction structure wherein the n-typecontact layer 103, the n-type cladding layer 104, the active layer 105,the p-type cladding layer 106 and the p-type contact layer 107 that areformed from gallium nitride compound semiconductor element are grown oneon another successively, the present invention is not limited to thisconstitution and it suffices to employ such a structure as at least theactive layer is capable of confining light in the direction of thicknesssandwiched by layers of higher refractive index (smaller band gap) thanthe active layer.

n-type and p-type optical guide layers may also be formed between then-type cladding layer 104 and the active layer 105 and between theactive layer and the p-type cladding layer 106.

Also the light emitting regions are formed in fan shape in the secondembodiment, but the present invention is not limited to thisconfiguration.

Moreover, while gallium nitride compound is used in the secondembodiment, the present invention is not limited to this configurationand other semiconductors such as GaAs or InGaP may be used.

Furthermore, although the pyramidal surface is formed in conical shapein the second embodiment, the present invention is not limited to thisconfiguration. For example, such a pyramidal surface may be employedthat consists of faces inclined so that light propagating in thewaveguide of the light emitting regions is refracted or reflected so asto be directed upward (perpendicular to the surface).

Also the second embodiment has been described by taking a particularstacked semiconductor structure as an example, but the present inventionis not limited to this constitution.

Besides the stacked semiconductor structure described above, forexample, such a stacked semiconductor structure may be employed asdescribed below: the buffer layer 102 having thickness of 200 Å made ofAlGaN, an undoped n-type GaN layer, the n-type contact layer 103 made ofGaN having total thickness of 4 μm doped with 2.5×10¹⁸/cm³ of Si, acrack prevention layer made of In_(x), Ga_(1−x)N (0.1≦x≦0.15) havingthickness of 1000 to 1500 Å, a cladding layer made of GaN, an n-typeguide layer having thickness of 2000 Å made of Si-doped (InGaN/GaN) ofsuper lattice structure, six sets of (GaN barrier layer/InGaN activelayer/GaN cap layer) for light emitting layer and a last barrier layermade of GaN are formed on the substrate 101 having a mask formedthereon. Then a p-type cap layer made of Al_(x)Ga_(1−x)N (0≦x≦0.35)doped with Mg having thickness of 100 to 350 Å, a p-type guide layerhaving thickness of 2000 Å or less made of Mg-doped (InGaN/GaN) of superlattice structure, a p-type cladding layer having thickness of 6000 Å orless made of Mg-doped GaN, and a p-type contact layer having thicknessfrom 150 to 200 Å made of Mg-doped p-type GaN may be formed successivelyinto stacked semiconductor structure.

Although the cavity 152 that is closed at the apex is formed below thelight emitting point 150 in the second embodiment, the present inventionis not limited to this configuration and a pyramidal cavity 152 b(having pyramidal surface 153 b) that opens at the top may be used asshown in FIG. 20.

Such a constitution with the cavity that opens at the top makes itpossible to emit light to the outside more efficiently than the closedcavity 152 (FIG. 21A) since light entering the cavity emerges to theoutside without being confined within the cavity as shown in FIG. 21B.

1. A point emission type light emitting element comprising: a striperidge having an n-type layer, an active layer and a p-type layer thatare formed from semiconductors on a substrate, so as to emit light fromone end face of the stripe ridge, wherein the stripe ridge has aprotruding portion on the end face and the surface of the light emittingelement is covered with a shading film except for the tip of theprotruding portion, and wherein the shading film comprises a materialselected from the group consisting of Cr/Ni, Cr, Ti/Pt, Ti, Ni, Al, Agand Au.
 2. The point emission type light emitting element according toclaim 1, wherein said n-type layer, said active layer and said p-typelayer comprise nitride semiconductor.
 3. The point emission type lightemitting element according to claim 1, wherein the width of the striperidge is in a range from 1 μm to 100 μm.
 4. The point emission typelight emitting element according to claim 1, wherein the width of theprotruding portion is in a range from 1 μm to 10 μm.
 5. The pointemission type light emitting element according to claim 1, wherein theridge stripe is formed by etching to a depth that does not reach theactive layer and the protruding portion is formed by etching to a depththat reaches the n-type layer.
 6. A point emission type light emittingelement comprising: a stripe ridge having an n-type layer, an activelayer and a p-type layer that are formed from semiconductors on asubstrate, so as to emit light from one end face of the stripe ridge,wherein the stripe ridge has a protruding portion on the end face andthe surface of the light emitting element is covered with a shading filmexcept for the tip of the protruding portion, and wherein the shadingfilm comprises TiO₂.
 7. The point emission type light emitting elementaccording to claim 6, wherein said n-type layer, said active layer andsaid p-type layer comprise nitride semiconductor.
 8. The point emissiontype light emitting element according to claim 6, wherein the width ofthe stripe ridge is in a range from 1 μm to 100 μm.
 9. The pointemission type light emitting element according to claim 6, wherein thewidth of the protruding portion is in a range from 1 μm to 10 μm. 10.The point emission type light emitting element according to claim 6,wherein the ridge stripe is formed by etching to a depth that does notreach the active layer and the protruding portion is formed by etchingto a depth that reaches the n-type layer.